Swing mouseEntered strange behavior

Question

I have a jframe with some JComponents, with some mouseListener. My aim is to show a little jframe with a specified text, when the mouse enter on a jlabel, and to show off it when the mouse is exited. Jframe is supposed to be shown near the mouse. Anyway that does not happen, and the programm behaves in a very strange way. Why? the bug That's my code

package finestrina;

import java.awt.GridLayout;
import java.awt.Point;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;

public class finestra implements MouseListener{

    private JFrame finestra = new JFrame();
    private JFrame pagina = new JFrame();
    private JButton submit1 = new JButton("press");
    private JTextField text = new JTextField();
    finestra(){

        pagina.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        pagina.setSize(500, 500);

        JPanel cont = new JPanel();
        cont.setLayout(new GridLayout(3,4));

            JLabel label = new JLabel();
            label.setText("ON MOUSEROVER THIS");
                cont.add(label);
            label.addMouseListener(this);   


            submit1.addMouseListener(this);
            text.addMouseListener(this);

        cont.add(submit1);
        cont.add(text);
        pagina.add(cont);
        pagina.setVisible(true);

        finestra.setUndecorated(true);
    }

    @Override
    public void mouseClicked(MouseEvent arg0) {}

    @Override
    public void mouseEntered(MouseEvent event) {
        if(event.getSource() instanceof JLabel){
            JLabel event_casted = (JLabel)event.getSource();

            if(event_casted.getText().equals("ON MOUSEROVER THIS")){
                Point punto = event.getLocationOnScreen();
                punto.setLocation(punto.getX()+20, punto.getY()+20);

                JLabel littlelabel = new JLabel();

                littlelabel.setText("your mouse is on the jlabel");
                finestra.add(littlelabel);
                finestra.setLocation(punto);
                finestra.setSize(100,100);
                finestra.setVisible(true);
            }
        }
    }

    @Override
    public void mouseExited(MouseEvent event) {
        if(event.getSource() instanceof JLabel){
            JLabel event_casted = (JLabel)event.getSource();
                if(event_casted.getText().equals("ON MOUSEROVER THIS")){
                    finestra.setVisible(false);
                }
        }
    }

    @Override
    public void mousePressed(MouseEvent event) {

    }

    @Override
    public void mouseReleased(MouseEvent arg0) {}

    public static void main(String[] args0){
        new finestra();
    };

}

Answer 1

There are a number of (possible) issues

• The GridLayout will cause the component to occupy most of the space of the container, which might cause the window to "appear" to popup earlier then you expect
• finestra.add(event_casted); is causing the label to be removed from it's current parent container (the main window), as a component can only belong to a single container

It would, generally be better to use the tooltip support provided by the API. Maybe have a look at How to Use Tool Tips , remember, they can also support HTML.

If that's not functionality what you want, then maybe a JPopupMenu might be better